[Qemu-devel] Re: [PATCH 1/8] use eventfd for iothread

[Pierre Riteau]

When this was merged in qemu-kvm/master (commit 
6249f61a891b6b003531ca4e459c3a553faa82bc) it removed Avi's compile fix when 
!CONFIG_EVENTFD (db311e8619d310bd7729637b702581d3d8565049).
So current master fails to build:
  CC    osdep.o
cc1: warnings being treated as errors
osdep.c: In function 'qemu_eventfd':
osdep.c:296: error: unused variable 'ret'
make: *** [osdep.o] Error 1

On 22 févr. 2010, at 22:26, Marcelo Tosatti wrote:

> From: Paolo Bonzini <address@hidden>
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Avi Kivity <address@hidden>
> ---
> osdep.c       |   32 ++++++++++++++++++++++++++++++++
> qemu-common.h |    1 +
> vl.c          |    9 +++++----
> 3 files changed, 38 insertions(+), 4 deletions(-)
> 
> diff --git a/osdep.c b/osdep.c
> index 9059f01..9e4b17b 100644
> --- a/osdep.c
> +++ b/osdep.c
> @@ -37,6 +37,10 @@
> #include <sys/statvfs.h>
> #endif
> 
> +#ifdef CONFIG_EVENTFD
> +#include <sys/eventfd.h>
> +#endif
> +
> #ifdef _WIN32
> #include <windows.h>
> #elif defined(CONFIG_BSD)
> @@ -281,6 +285,34 @@ ssize_t qemu_write_full(int fd, const void *buf, size_t 
> count)
> 
> #ifndef _WIN32
> /*
> + * Creates an eventfd that looks like a pipe and has EFD_CLOEXEC set.
> + */
> +int qemu_eventfd(int fds[2])
> +{
> +    int ret;
> +
> +#ifdef CONFIG_EVENTFD
> +    ret = eventfd(0, 0);
> +    if (ret >= 0) {
> +        fds[0] = ret;
> +        qemu_set_cloexec(ret);
> +        if ((fds[1] = dup(ret)) == -1) {
> +            close(ret);
> +            return -1;
> +        }
> +        qemu_set_cloexec(fds[1]);
> +        return 0;
> +    }
> +
> +    if (errno != ENOSYS) {
> +        return -1;
> +    }
> +#endif
> +
> +    return qemu_pipe(fds);
> +}
> +
> +/*
>  * Creates a pipe with FD_CLOEXEC set on both file descriptors
>  */
> int qemu_pipe(int pipefd[2])
> diff --git a/qemu-common.h b/qemu-common.h
> index b09f717..c941006 100644
> --- a/qemu-common.h
> +++ b/qemu-common.h
> @@ -170,6 +170,7 @@ ssize_t qemu_write_full(int fd, const void *buf, size_t 
> count)
> void qemu_set_cloexec(int fd);
> 
> #ifndef _WIN32
> +int qemu_eventfd(int pipefd[2]);
> int qemu_pipe(int pipefd[2]);
> #endif
> 
> diff --git a/vl.c b/vl.c
> index 98918ac..1957018 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3211,14 +3211,15 @@ static int io_thread_fd = -1;
> 
> static void qemu_event_increment(void)
> {
> -    static const char byte = 0;
> +    /* Write 8 bytes to be compatible with eventfd.  */
> +    static uint64_t val = 1;
>     ssize_t ret;
> 
>     if (io_thread_fd == -1)
>         return;
> 
>     do {
> -        ret = write(io_thread_fd, &byte, sizeof(byte));
> +        ret = write(io_thread_fd, &val, sizeof(val));
>     } while (ret < 0 && errno == EINTR);
> 
>     /* EAGAIN is fine, a read must be pending.  */
> @@ -3235,7 +3236,7 @@ static void qemu_event_read(void *opaque)
>     ssize_t len;
>     char buffer[512];
> 
> -    /* Drain the notify pipe */
> +    /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
>     do {
>         len = read(fd, buffer, sizeof(buffer));
>     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
> @@ -3246,7 +3247,7 @@ static int qemu_event_init(void)
>     int err;
>     int fds[2];
> 
> -    err = qemu_pipe(fds);
> +    err = qemu_eventfd(fds);
>     if (err == -1)
>         return -errno;
> 
> -- 
> 1.6.6
> 
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-- 
Pierre Riteau -- PhD student, Myriads team, IRISA, Rennes, France
http://perso.univ-rennes1.fr/pierre.riteau/